214 NATURE STUDY AND LIFE 



interesting calculation as to the number that might arise 

 from a single parent for a season or a year, and it will 

 open the eyes of the pupils to the necessity of prompt 

 action if they hope to prevent injury to their plants. 

 The mathematician Reaumur estimated that in five gen- 

 erations, which might not require more than ten weeks, 

 a single aphid could become the mother of 6,000,000,- 

 000,000. For the corn-root aphid Professor Forbes has 

 calculated that a " stem mother," as the fertile females are 

 called, might produce in a season 9,500,000,000,000 young. 

 Placed end to end these would form a procession 7,850,000 

 miles in length, a distance equal to 314 times the earth's 

 circumference ; or, standing shoulder to shoulder, they 

 would make an army 10 feet wide and 230 miles long. 

 Nothing in nature shows more clearly what an infinite 

 power for harm a little thing may be. 



Local conditions and interests should largely determine 

 the species of aphids to be studied. 



The grape phylloxera, P. vastatrix, is the insect which 

 has devastated the vineyards of Europe, but it is not 

 so destructive among the native grapes of this country. 

 It exists in two forms, one infesting the leaves, the other 

 the roots. In both locations the aphids cause knotty, 

 wartlike galls, often conspicuous on the underside of 

 grape leaves and also found on the finer rootlets. By 

 cutting these galls open we may find the insects them- 

 selves. Plucking and burning the leaves as soon as the 

 galls appear is the simplest remedy suggested, and any 

 young vine with lumpy nodules on its roots had better be 

 burned than planted. A little " sharp-eye " study of the 

 grapevines about their homes will soon determine whether 



